<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
	String path = request.getContextPath();
	String basePath = request.getScheme() + "://"
			+ request.getServerName() + ":" + request.getServerPort()
			+ path + "/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
	<head>
		<base href="<%=basePath%>">

		<title>My JSP 'calculate.jsp' starting page</title>

		<meta http-equiv="pragma" content="no-cache">
		<meta http-equiv="cache-control" content="no-cache">
		<meta http-equiv="expires" content="0">
		<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
		<meta http-equiv="description" content="This is my page">
		<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

	</head>

	<body>
		${1+2 }
		<br />
		<%--${"abc"+"bcd"}加号不是字符串连接，会报错 --%>
		<%
			request.setAttribute("str", "ac");
			request.setAttribute("s", "");
			request.setAttribute("list",new ArrayList());
			Object o = null;
			request.setAttribute("o",o);
		%>
		${str}<br>
		${str=="ac"}
		<br>
		<%--empty运算 --%>
		<%--为true的情况 
  	空字符串
  	List中无数据
  	找不到
  	null
  --%>
		${empty s }		<br />
		${empty list }<br>
		${empty zhaobudao }<br>
		${empty o }
	</body>
</html>
